The collection of physical evidence is an important aspect to any investigation. This activity encourages the students to develop observation, hand lens/microscope and data collection skills. Students will observe, describe, compare and classify various cloth stains and hair samples. By this point in the unit students should be comfortable with the process of completing and activities and recording their results to your satisfaction. The emphasis should be on students making precise descriptions and clear diagrams of their observations. With the assistance of a hand lens or microscope, students should be able to observe and identify the characteristics in stains and hair samples
Part 1 - Cloth Fibers
Students are given a piece of cloth and are asked to record their observations using their eye and with a hand lens/microscope. The emphasis should be on recording as many details about the cloth as possible. This may be difficult for some, but have students focus on texture of cloth, arrangement of fibers in the cloth and any other unique features. In Part 2 they will have to use these observations and notes to determine how the stain is different from the cloth. Note that students are now being asked to construct their own tables and make their own notes rather than being asked to provide this information.
Part 2 - Identifying Unknown Stains
One important aspect of this part of the activity is to ensure that the stains are all different in composition, but look similar appearance. As well, the differences in the stains should be at the hand lens/microscopic level to ensure that the students can't differentiate between the stains at the normal eye level. The following three stains put onto red cloth has worked well.
Finally the students will observe an unknown stain and match it to one of the three known stains. Use another type of material so as the students observe the stains characteristics rather than the characteristics of the cloth. Have all three stains on different pieces of cloth and each unknown stain numbered. This will ensure that students make their own observations, rather than "borrowing" someone else's notes.
Part 3 - Hair Analysis
Regardless of the age, students appear to enjoy looking at samples of hair under the microscope. The intent of Part 3 is to have students draw and describe at least two different strands of hair. To complete this task it will be necessary to have students use a microscope. It is assumed that you will have reviewed appropriate use of the microscope and how to make a wet mount slide to view the hair.
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